Project Abstract Acute myocardial infarction and resulting ischemic heart disease are the single most prevalent cause of morbidity and mortality in the western world. While the bioactive glycerophospholipid lysophosphatidic acid (LPA) plays a well-known role in atherosclerotic disease, its role in myocardial function remains virtually unexplored. Following acute myocardial infarction, serum LPA concentration rises by six-fold over control subjects, suggesting LPA may contribute to the pathogenesis of myocardial infarction. LPA production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin, whereas lipid phosphate phosphatase-3 (LPP3) catalyzes LPA dephosphorylation to generate lipid products that are not receptor active. In this application, we present the first evidence that cardiac ischemia/reperfusion (I/R) injury enhances myocardial autotaxin levels and decreases myocardial LPP3 expression, and this is associated with increased serum LPA levels. Upon reperfusion, reactive oxygen species production arises as a burst of superoxide from mitochondria following I/R injury. The redox-sensitive transcription factor NFAT (a nuclear factor of activated T- cells) has been shown to bind to the autotaxin promoter and induce its expression. Similarly, oxidant stress may deplete LPP3 levels in the context of I/R injury through reduced LPP3 expression or enhanced LPP3 degradation. Thus, we hypothesize that I/R injury alters autotaxin and LPP3 expression through mitochondrial superoxide production to drive LPA signaling and cardiomyocyte dysfunction. The following interrelated specific aims are designed to provide step-wise and in-depth studies in vitro, in vivo, and in experimental therapeutics settings. Specific aim 1 will assess the role of myocardial superoxide production in autotaxin expression and LPA production in I/R injury metabolism. Specific aim 2 will determine the role of mitochondrial superoxide production in LPP3 depletion and LPA production in I/R injury. We could identify whether modulation of cellular versus mitochondrial antioxidant status confers a differential protective effect in I/R injury models.